Field of the Invention
The present invention relates to a control apparatus for an automatic transmission.
Description of the Related Art
An automatic transmission generally includes planetary gear mechanisms and engaging mechanisms such as a clutch and a brake, and implements each gear range by switching the power transmission path by the engaging mechanisms. As the engaging mechanisms, employing a mechanical engaging mechanism has been proposed in addition to a hydraulic engaging mechanism. In particular, an arrangement that uses a clutch (two-way clutch) capable of switching to a state to do two-way rotation restriction as a brake has been proposed (for example, Japanese Patent Laid-Open No. 2014-202340).
When the two-way clutch is used as a brake, a rotational element connected to the two-way clutch can be switched between a state in which rotation is restricted only in one direction (rotation in the reverse direction is permitted) and a state in which rotation is restricted in both directions. When switched to the state in which rotation is restricted in both directions, the rotational element connected to the two-way clutch is fixed to the casing. For this reason, if switching is done during rotation of the rotational element, unusual noise or vibration occurs, and the two-way clutch breaks. To prevent this, switching may be performed via an engaging combination that brings the rotational element to a standstill.
However, if establishment of the engaging combination that brings the rotational element to a standstill takes time, switching of the gear range may take time. On the other hand, if the vehicle is at rest or has a very low speed, the rotation speed of each rotational element of the planetary gear mechanisms is low, and unusual noise or vibration is small.